The frequent detection of polar organic micropollutants such as pesticides, consumer care products or pharmaceutical in water is an increasing concern for human and ecosystem health. Currently, little is known about the long-term fate of such compounds in aquatic systems due to the difficulty in demonstrating their degradation.

Compound-specific isotope analysis (CSIA) of multiple elements has become a well-established method to identify and quantify degradation pathways for classical priority pollutants such as chlorinated and petroleum hydrocarbons. The extension of the CSIA approach to micropollutants however is challenging for several reasons: micropollutants are typically present in lower concentrations thus requiring more extensive preconcentration, they often are more polar hence requiring derivatization before gas chromatographic analysis, they frequently include heteroatoms complicating their conversion to measurement gases for mass specrometry, and they are geraded by a wide range of mechanisms, whose isotope effects are not known yet.

The main goal of this project is to extend the CSIA approach for assessing degradation pathways to polar organic micropollutants.

Pesticide degradation in agricultural soils and vadose zone is being studied in field based lysimeter experiments and the analysis of C, N and Cl isotopes of the target compounds is being developed in collaboration with the Institute of Groundwater Ecology of the Helmholtz Zentrum München, the Swiss Federal Institute of Aquatic Science and Technology EAWAG and the Agroscope Institute for Sustainability Sciences ISS.

Chlorinated solvents are ubiquiotous groundwater contaminants. They have benn heavily used in the 1940s-1970s in dry-cleaning factories, for their degreasing properties in the car and watch industry or as solvents in the chemical industry. Their inappropriate disposal and accidental spills lead to a great number of contaminated sites in developed countries. In Switzerland alone, 7000 former industrial sites were estimated to be polluted with chlorinated solvents, among which an estimated 1100 sites will probably require cleaning up. As DNAPLs, the estimation of chlorinated solvents fate represents a challenge.

Compound-specific isotope analysis (CSIA) has been increasingly used to track reactive processes affecting chlorinated solvents in aquifer systems. This method makes use of isotope effects associated with (bio)degradation processes. However, recent studies have demonstrated that isotope fractionation also occurs during physical processes. Therefore, beside improving the comprehension of reactive processes (Advocate Project) also physical processes and its isotope effects are investigated (Diffusion Project) to improve the application of compound-specific isotope analysis for tracking reactive processes impacting chlorinated solvents in the subsurface.

Stable isotope applications for hydro-climatic reconstructions

Current climatic changes raise the question about the natural variability of the climate system in the past. An enhanced understanding of these natural climate dynamics is essential for refining climate projections for the future. Sediment sequences provide the possibility to study past changes using sedimentological and biogeochemical tools.

We are particularly interested in the variation and the forcing of the hydro-climate in the Alpine and Mediterranean area during the late Pleistocene and the Holocene (past ~15,000 years). Currently, we study the potential and the climatic meaning of the H isotope composition of plant waxes archived in lake sediments. Due to the expected complex forcing of temperature, precipitation, and moisture-source changes, this method has – in contrast to low-latitude study areas – not yet established in the Alpine region. As a complement, we also study the climatic and hydrological control of the O isotope composition of carbonate phases in lake sediments.